Open label, 48-week pilot study to evaluate the effects of highly active antiretroviral therapy (haart) consisting of ritonavir (rtv, zidovudine (adv), and lamivudine (#tc) on several immunologic and virologic parameters. sample size: 55 evaluable subjects with moderately advanced, HIV-1 infection; population; eligible males and females at least 16 years of age who have a cd4 cell count between 100-300 cells/mm3, and have previously\tolerated three consecutive onths of zdv therapy at doses ranging from 500-6-- mg per day but have never received 3tc or a protease inhibitor. Regiment: eligible subjects will initiate the following treatment regimen: ritonavir 300 mg bid for two days, then ritonavir 400 mg bid for two days, then ritonavir 500 mg bid for two days, athens ritonavir 600 mg bid fore three days. All subjects must initiate zdv (200 mg tid) and lamivudine (150 mg bid) on study day 10 and through week 48 the treatment regimen should consist of ritonavir 600 mg bid, plus zidovudinnne 200 mg tid, plus lamivudine 150 mg bid. In addition, study treatment will be extended to allow subjects who complete 48 weeks of therapy to remain on study treatment until approximately the final- enrolled subject completes 48 weeks of haart. The treatment-extension period is implemented in anticipation of a rollover protocol.